[PATCH RFC 04/11] rust: siphash: Add a simple siphash abstraction

Asahi Lina
2023-07-14T09:32:26Z

This simple wrapper allows Rust code to use the Hasher interface with
the kernel siphash implementation. No fancy features supported for now,
just basic bag-of-bytes hashing. No guarantee that hash outputs will
remain stable in the future either.

Signed-off-by: Asahi Lina <lina@asahilina.net>
---
rust/bindings/bindings_helper.h | 1 +
rust/helpers.c | 8 ++++++++
rust/kernel/lib.rs | 1 +
rust/kernel/siphash.rs | 39 +++++++++++++++++++++++++++++++++++++++
4 files changed, 49 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 3e601ce2548d..52f32e423b04 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -10,6 +10,7 @@
#include <linux/slab.h>
#include <linux/refcount.h>
#include <linux/wait.h>
+#include <linux/siphash.h>
#include <linux/sched.h>

/* `bindgen` gets confused at certain things. */
diff --git a/rust/helpers.c b/rust/helpers.c
index bb594da56137..1ed71315d1eb 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -24,6 +24,7 @@
#include <linux/errname.h>
#include <linux/refcount.h>
#include <linux/mutex.h>
+#include <linux/siphash.h>
#include <linux/spinlock.h>
#include <linux/sched/signal.h>
#include <linux/wait.h>
@@ -135,6 +136,13 @@ void rust_helper_put_task_struct(struct task_struct *t)
}
EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);

+u64 rust_helper_siphash(const void *data, size_t len,
+ const siphash_key_t *key)
+{
+ return siphash(data, len, key);
+}
+EXPORT_SYMBOL_GPL(rust_helper_siphash);
+
/*
* We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
* as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 85b261209977..8fb39078b85c 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -36,6 +36,7 @@
pub mod ioctl;
pub mod prelude;
pub mod print;
+pub mod siphash;
mod static_assert;
#[doc(hidden)]
pub mod std_vendor;
diff --git a/rust/kernel/siphash.rs b/rust/kernel/siphash.rs
new file mode 100644
index 000000000000..e13a17cd5a93
--- /dev/null
+++ b/rust/kernel/siphash.rs
@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A core::hash::Hasher wrapper for the kernel siphash implementation.
+//!
+//! This module allows Rust code to use the kernel's siphash implementation
+//! to hash Rust objects.
+
+use core::hash::Hasher;
+
+/// A Hasher implementation that uses the kernel siphash implementation.
+#[derive(Default)]
+pub struct SipHasher {
+ // SipHash state is 4xu64, but the Linux implementation
+ // doesn't expose incremental hashing so let's just chain
+ // individual SipHash calls for now, which return a u64
+ // hash.
+ state: u64,
+}
+
+impl SipHasher {
+ /// Create a new SipHasher with zeroed state.
+ pub fn new() -> Self {
+ SipHasher { state: 0 }
+ }
+}
+
+impl Hasher for SipHasher {
+ fn finish(&self) -> u64 {
+ self.state
+ }
+
+ fn write(&mut self, bytes: &[u8]) {
+ let key = bindings::siphash_key_t {
+ key: [self.state, 0],
+ };
+
+ self.state = unsafe { bindings::siphash(bytes.as_ptr() as *const _, bytes.len(), &key) };
+ }
+}

--
2.40.1